So sorry to hear that you are having foot problems! They are a real bummer. Unfortunately I've had to soak many, MANY feet. (I work with racehorses) We use a shallow ground feeder, the flexible rubber kind. If you are soaking for an abcess, the water does not need to be crazy deep. The shallow feeders are awesome because if they step out of it they are less likely to knock it over/get caught in it. They don't make a huge CRASH!BANG! Noise if they get knocked over either. All I can say is to keep putting the foot back in, over and over. Feed him treats to keep him occupied, or just brush and love on him. The water does not need to be much over the hairline if using epsom salts. If you are using the blue stuff, don't let the water go over the hair at all, as it can blister.
I've never heard of the Davis boot as the PP suggested, but it seems pretty cool! The Jim Rickens is awesome stuff - but I've never used it for abcess before. We use it as a hardener/desensitizer. Don't get it on your skin as it stings and stains, and it smells horrible. Apply it with an old toothbrush to the sole only, and make sure the foot is dry. It's iodine based (I believe) and it stings the eyes when it meets with water. I spilled a bottle of it at the races one night and everyone was giving me the stink eye!
Good luck with the soaking - keep us updated!